چكيده به لاتين
Successful operation of circuit breakers is vital to the power systems operation and protection, so their design and operation improvement deserve particular importance. Therefore, accurate modeling and performance improvement of single-pressure gas circuit breakers has been selected as the main purpose of this dissertation. Thermal and dielectric regimes of circuit breaker’s operation have been studied. So far no comprehensive study has been conducted on the prestrikes in SF6 circuit breakers. A multi-physics model is developed to accurately modeling the prestrikes in SF6 circuit breakers. In this study, a model is developed for a simultaneous solution of the MHD equations and the governing equations of the electric circuit feeding the plasma in order to consider mutual effects of the electric circuit and the plasma. Navier-Stoke equations, turbulent flow equations, and the equation of heat transfer in fluids, coupled with Maxwell's equations are physical equations governing the circuit breakers. Kirchhoff's voltage and current laws equations are governing equations of the external electric circuit. Finite Element Method (FEM) is used to solve the multi-physics equations governing the circuit breaker. A 72.5 kV single pressure puffer type SF6 circuit breaker is used for numerical studies. To investigate the mutual effects of the feeding circuit parameters and generated plasma in the circuit breaker, numerical studies are performed for different values of resistance and inductance in the arc current path. In order to investigate the effects and importance of the arcing contact shape on the prestrike in SF6 gas CBs, three different types of arcing contacts are investigated in this thesis. Since changing the refill valve diameter can alter the direction of the SF6 gas motion in the closing CB, understanding its effects on CBs function and performance may help to improve the CB design. This thesis has focused on the effects of refill valve diameter on prestrike occurrence in the closing of puffer type SF6 CBs. Numerical studies show that the refill valve diameter has a considerable influence on the prestrike occurrence instant.
